Mo₂N nanobelt cathodes for efficient hydrogen production in microbial electrolysis cells with shaped biofilm microbiome

High cost platinum (Pt) catalysts limit the application of microbial electrolysis cells (MECs) for hydrogen (H₂) production. Here, inexpensive and efficient Mo₂N nanobelt cathodes were prepared using an ethanol method with minimized catalyst and binder loadings. The chronopotentiometry tests demonstrated that the Mo₂N nanobelt cathodes had similar catalytic activities for H₂ evolution compared to that of Pt/C (10 wt%). The H₂ production rates (0.39 vs. 0.37 m³-H₂/m³/d), coulombic efficiencies (90% vs. 77%), and overall hydrogen recovery (74% vs. 70%) of MECs with the Mo₂N nanobelt cathodes were also comparable to those with Pt/C cathodes. However, the cost of Mo₂N nanobelt catalyst ($ 31/m²) was much less than that of Pt/C catalysts ($ 1930/m²). Furthermore, the biofilm microbiomes at electrodes were studied using the PacBio sequencing of full-length 16S rRNA gene. It indicated Stenotrophomonas nitritireducens as a putative electroactive bacterium dominating the anode biofilm microbiomes. The majority of dominant species in the Mo₂N and Pt/C cathode communities belonged to Stenotrophomonas nitritireducens, Stenotrophomonas maltophilia, and Comamonas testosterone. The dominant populations in the cathode biofilms were shaped by the cathode materials. This study demonstrated Mo₂N nanobelt catalyst as an alternative to Pt catalyst for H₂ production in MECs.